1. Field of the Invention
The invention relates to an exhaust-gas turbocharger with variable turbine geometry, a regulating device for an exhaust-gas turbocharger as well as a vane lever for a regulating device of an exhaust-gas turbocharger.
2. Discussion of the Related Art
In turbo machines in which the turbine drives the compressor or charger it is often advantageous to regulate the exhaust-gas stream going into the turbine to improve efficiency, responsiveness or the operating range. This can be achieved by a variable geometry of the nozzle channels leading to the turbine wheel. These nozzle channels with variable geometry can be generated by a ring of pivotable guide vanes, which allow adjusting the channels in between themselves. The construction of the regulating device driving the pivotable vanes is crucial to prevent the vanes or the regulating device from seizing.
U.S. Pat. No. 2,860,827 and U.S. Pat. No. 4,179,247 show proposals how to prevent seizing of the regulating device for the guide vanes. However, neither of the two constructions is suitable for the temperature variations as they occur in modern combustion engines within the turbine housing or the components of the regulating device. Moreover the bearing assembly of U.S. Pat. No. 4,179,247 is comparatively complicated to assemble.
From the company's internal state of the art an exhaust-gas turbocharger with variable turbine geometry is known. It is shown in FIG. 9 through 12.
The principle construction of this exhaust-gas turbocharger according to the company's internal state of the art is illustrated in FIG. 9. Components of the exhaust-gas turbocharger according to FIG. 9 which are important for the comprehension of the invention described below are illustrated in FIG. 10 through 12.
The exemplary exhaust-gas turbocharger (1) according to the company's internal state of the art features a housing consisting of a bearing housing (3) and turbine housing (2), with a pivoting shaft (4). On one end the shaft (4) carries the compressor wheel (33) and on its other end the turbine wheel (5). Within the turbine housing (2) on the side of the turbine wheel (5) a volute (6) is formed which in radial direction evolves into a throat (7). Inside the throat (7) adjustable guide vanes are located.
The guide vanes (8) are pivoted from a vane bearing ring (12) and from a thrust- and bearing-ring (28) which is by a spacer (29) kept at a certain distance from the bearing ring (12), and they are adjustable through an actuator (32) which actuates the unison ring (9). A rotary motion of the unison ring (9) with respect to the vane bearing ring (12) is transmitted onto the guide vanes (8) which by this means can be adjusted within a pre-determined range between the open and closed position. The entire regulating device including all its components will be referred to as guide apparatus (13).
The flow channels of the circular throat (7) in which the exhaust gas flows radially are constituted by the spacing between the guide vanes (8). Through variation of the angular position of the guide vanes (8) the flow channels are adjustable.
FIGS. 10 through 12 show the guide vanes (8) which are mounted to the vane bearing ring (12) by means of vane studs (18), which penetrate the vane bearing ring (12) and which carry a vane lever (11) on the end opposing the guide vanes (8).
The unison ring (9) which serves the simultaneous actuation of all the vane levers (11) is located within the axial plane of the circular arranged vane levers (11) above. For the actuation of all vane levers (11) the unison ring (9) features engaging means on its inner rim which interact with suitable engaging means on each of the vane levers (11) such that during rotation of the unison ring (9) with respect to the vane bearing ring (12) all vane levers (11) and therewith the guide vanes (8) are simultaneously rotated.
The unison ring (9) carries as means for the actuation an actuator lug (15) which is connected to the actuator (32) enabling the adjustment of the unison ring (9) from outside of the housing.
As illustrated in FIGS. 11 and 12 the unison ring (9) is supported by six rollers (31), which serve the radial guidance of the unison ring (9).
The rollers (31) in turn are held in position by a cage (30) which is pivoted inside the turbine housing (2). The cage (30) features bores in which the rollers (31) are pivoted.
This arrangement functions satisfactorily as long as there are no major temperature variations. However modern exhaust-gas turbochargers are exposed to extreme temperature variations. The turbine components and adjacent parts can reach temperatures as high as 900° C. These temperature changes in connection with the extremely high revolution speed of the turbine wheel and the compressor wheel strain all the components and result in a high level of wear and in the worst cast failure of the exhaust-gas turbocharger.
In this context it is of high importance to keep the geometric arrangement of all interacting parts like vane bearing ring, unison ring, rollers, vane studs, actuator lugs etc. constant at a level which allows adjusting the guide vanes under all temperature and operational conditions.
From EP 1 357 255 A1, which is the bases for the invention, an exhaust-gas turbocharger with a guide apparatus with a ring of adjustable guide vanes is known. The guide vanes are pivoting on a vane bearing ring by means of vane studs.
The vane studs penetrate the vane bearing ring axially. They are one to one torque proof connected to one of the guide vanes as well as one of the vane levers.
In order to reduce wear during large temperature variations while maintaining a simple design EP. 1 357 255 A1 proposes to support the unison ring through the vane lever radially. In a preferable embodiment the vane levers feature axial lugs serving as radial bearing. In this case a rolling movement between the unison ring and the radial bearing area occurs.
Although this style of radial support of the unison ring with axial lugs of the vane levers has basically proven to be robust, further improvements are desirable.